Sounds like you answered your own question...
Oh... I misread your question. I thought you were asking about 3CX syncing your Office 365 contacts to your Android/mobile phone address book. I haven't played with the Office 365 sync but what you can test is making a manual contact in the management console and seeing if that syncs to your T29G. Then you'll know if it's a problem with the address book in general or just not syncing O365 contacts.
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.